This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 11(1999)-320228 filed on Nov. 10, 1999, Japanese Application No. 11(1999)-320631 filed on Nov. 11, 1999, Japanese Application No. 11(1999)-322394 filed on Nov. 12, 1999 and Japanese Application No. 11(1999)-322396 filed on Nov. 12, 1999, the entire content of all of which is incorporated herein by reference.
This invention generally relates to vehicle brake systems. More particularly, the present invention pertains to a brake master cylinder for a vehicle brake system.
Japanese Utility Model Publication No. 8(1996)-1997 describes a brake master cylinder that includes a body having an internal bore opening at a rear end, a cylinder cap assembled at an internal bore opening portion of the body and forming a cylinder housing with the body, a first piston positioned in the cylinder housing through the cylinder cap and slidably supported in the axial direction by a first cylindrical guide assembled in the cylinder cap, a second piston positioned coaxially with the first piston at the front of the first piston and axially slidable in the cylinder housing, and a cup seal sealing in a liquid-tight manner a first pressure chamber formed between the first piston and the second piston at the front of the guide (tandem type master cylinder).
The first guide slidably supporting the first piston in the axial direction is coaxially engaged with the internal bore of the cylinder cap, a sleeve slidably supporting the first piston and the second piston in the axial direction at the front of the first guide is coaxially engaged with the internal bore of the cylinder cap, and the cup seal liquid-tightly sealing the first pressure chamber formed between the first piston and the second piston at the front of the guide is coaxially engaged with an internal bore provided at a rear end of the sleeve. The sleeve is disposed in the cylinder cap via the first guide at the rear end, and is disposed in the body via a second guide slidably supporting the second piston in the axial direction at the front end. The sleeve is supported along with both guides by the body and the cylinder cap, and the cylinder cap is fixed to the body by a screw connection.
Japanese Patent Laid-Open Publication No. H11-198794 discloses a brake master cylinder in which a guide (piston guide portion) slidably supporting a first piston in the axial direction at the rear of a cup seal is provided in one unit with an inner peripheral portion of a cylinder cap, and a first communication conduit (a conduit communicating with a piston part at a retracted position of the first piston) is provided on an inner peripheral portion of the guide. The first communication conduit is structured with a straight internal bore formed at the front inner periphery of the guide and a tapered internal bore wherein a diameter thereof is gradually enlarged from the rear end of the straight bore in the rear direction of the straight internal bore.
A second communication conduit (a conduit communicating the first communication conduit and an annular conduit formed on the body and the cylinder cap) provided on the cylinder cap is constructed with a first communication bore opening to the outer periphery surface of the cylinder cap, communicating with the annular conduit, and extending straight towards the inner periphery at a predetermined tilt angle relative to the central axis of a first piston and a second communication bore communicating by opening to the middle of the tapered internal bore of the first communication conduit. The second communication bore communicates with the first communication bore by extending straight towards the outer periphery with a tilt angle larger than that of the first communication bore.
In this brake master cylinder disclosed in Japanese Patent Laid-Open Publication No. H06-298072, a first seal member (O-ring) blocking the communication between an annular conduit and the atmosphere at the rear of the annular conduit is assembled at a first annular groove provided on the outer periphery of the cylinder cap. A second seal member (an O-ring whose diameter is smaller than that of the first seal member) is positioned at a second annular groove provided on the outer periphery of the cylinder cap.
The Japanese Utility Model Application published as Jitsu-kai-hei 5(1993)-80945 discloses a brake master cylinder in which an annular seal member is assembled at an annular recess portion provided on a cylinder cap at the rear of a guide. The seal member provides an air-tight and liquid-tight seal between the cylinder cap and a first piston. The recess portion of the cylinder cap is open to the front (open to both the front and rear), is in communication with an accommodation bore accommodating the guide, and is in communication with a second communication conduit provided with the cylinder cap via a communication groove formed on the rear end face of the guide with a fluid chamber formed with the seal member at the rear of the guide.
In the brake master cylinder described in the Japanese Utility Model Publication published as Jitsu-kai-hei 8(1996)-1997, the guide slidably supporting the first piston in the axial direction is coaxially engaged with the internal bore of the cylinder cap and the cup seal liquid-tightly sealing the first pressure chamber formed between the first piston and the second piston at the front of the guide is coaxially engaged with the internal bore of the sleeve coaxially engaged with the internal bore of the cylinder cap. Accordingly, it is difficult to improve the assembling precision of the guide and the cup seal and the cocentricity of the cup seal and the first piston supported by the guide.
Because the sleeve is inserted into and supported by the body, and the cylinder cap is connected to the body with screws along with both guides, the axial length of the sleeve and both guides should be designed to have sufficient length. Accordingly, the expanding and contracting amount of the sleeve and both guides that is generated due to the change of the surrounding temperature becomes large, and a looseness at the screw connecting portion of the body and the cylinder cap may be generated. When the cylinder cap is excessively tightened to prevent the generation of the looseness of the screw connecting portion, excessive load is added to the entire sleeve and both guides. As a result, a material possessing high durability is required to be adopted for the sleeve and both guides. This increases the manufacturing cost and may interfere with the assembling precision of the cup seal by deformation of the internal bore provided at the rear end of the sleeve in which the cup seal is disposed.
In the brake master cylinder described in Japanese Patent Laid-Open Publication No. H11-198794, because the second communication conduit is structured with the first communication bore and the second communication bore, and the second communication bore opens in the middle of the tapered internal bore, brake fluid flow from the reservoir to the first communication conduit via the reservoir connecting point and the annular conduit flows into this first pressure chamber through the first communication bore and the second communication bore of the second communication conduit and the small diameter portion of the tapered internal bore and the straight internal bore of the first communication conduit. Accordingly, brake fluid does not flow appropriately into a large diameter portion of the tapered internal bore wherein the air left in the large diameter portion of the tapered internal bore cannot be appropriately relieved and so air remains in the large diameter portion.
In the brake master cylinder disclosed in Japanese Patent Laid-Open Publication No. H11-198794 in which a bypass conduit opens to the large diameter portion of the tapered internal bore at the rear end and opens to a back face of the cup seal at the front end, when negative pressure is generated in the first pressure chamber the remaining air in the large diameter portion of the tapered internal bore is relieved to the first pressure chamber along with the accompanying brake fluid to supply the brake fluid from the reservoir to the large diameter portion of the tapered internal bore into the first pressure chamber via a lip portion of the cup seal and the bypass conduit. However, the structure of the first communication conduit and the second communication conduit is still susceptible of improvement.
The first communication bore and the second communication bore included in the second communication conduit are easily processed or produced by drill processing. However, in order to accurately connect and provide communication between the first communication bore and the second communication bore by aligning the rear end (internal end) of the first communication bore with the front end (external end) of the second communication bore, the drill processing position of the first communication bore and the second communication bore need to be aligned. This requires relatively high processing precision and can lead to an increase in the manufacturing cost.
In the master cylinder described in Japanese Patent Laid-Open Publication No. H06-298072, because the tilted communication bore constructed as a part of the second communication conduit is provided at the inner peripheral side compared to the first annular groove and it is necessary to ensure sufficient thickness between the tilted communication bore and the first annular groove, the size of the outer diameter of the cylinder cap is enlarged, thus enlarging the body. This presents an obstacle to reducing the size and weight of the brake master cylinder.
Considering the cylinder cap of the brake master cylinder described in Japanese Patent Laid-Open Publication No. H06-298072, each seal member assembled to each annular groove of the cylinder cap moves forward during slidable rotational contact of the inner periphery of the internal bore of the body with the outer periphery of the seal. Accordingly, each seal member may be bent or twisted to deteriorate the sealing function. Also, the diameter of the first seal member is larger than that of the second seal member and the probability that the first seal member is bent is higher than the second seal member.
In the brake master cylinder described in the Japanese Utility Model Application published as Jitsu-kai-hei 5(1993)-80945, the load according to the pressure of the first pressure chamber acts on the guide and is accepted by the cylinder cap after acting from the rear end of the guide to the cylinder cap. The rear end of the guide contacts the cylinder cap at the annular portion between the outer diameter of the guide and the outer diameter of the recess portion provided on the cylinder cap. When the seal member with a large diameter is adopted, the outer diameter of the recess portion is enlarged. It may thus not be possible to ensure the contacting area (load receiving portion area) between the rear end of the guide and the cylinder cap. In this case, the guide receiving an excess load may damage the rear end of the guide due to an excessive compression at the contact portion with the cylinder cap and may deform and damage the inner periphery portion of the guide to the recess portion of the cylinder cap. The damage on the guide can be prevented by strengthening the guide itself. However, utilizing materials having the necessary high strength undesirably increases the manufacturing cost.
Accordingly, a need exists for an improved brake master cylinder which overcomes at least the above-noted drawbacks.
A need also exists for a brake master cylinder having improved performance and reduced manufacturing cost.
In the brake master cylinder of the present invention, the guide member is coaxially engaged with the internal bore of the cylinder cap and the cup seal is coaxially engaged with the internal bore of the cylinder cap. Because the guide and the cup seal are coaxially engaged with the internal bore of the cylinder cap, the assembling precision of the guide and the cup seal and the concentricity of the cup seal and the first piston supported by the guide can be easily improved and the sealing effects between the first piston and the cup seal can also be improved. More particularly, upon assembly, the bore diameters of the guide and the cup seal at the internal bore of the cylinder cap are identical or the same, and so the bore processing of the cylinder cap is easily carried out and the assembly error of the guide and the cup seal into the cylinder cap internal bore can be reduced to improve the concentricity of the first piston and the cup seal.
Another aspect of the present invention involves the brake master cylinder being designed so that at least a part of the sleeve slidably supporting the first piston and the second piston in the axial direction is coaxially engaged with the internal bore of the cylinder cap at a front of the guide and the cup seal. When at least a part of the sleeve slidably supporting the first piston and the second piston in the axial direction is coaxially engaged with the internal bore of the cylinder cap at the front of the guide and the cup seal, the assembly precision with respect to the guide, the cup seal, and the sleeve can be easily improved to also easily improve the sliding performance of the first piston supported by the guide and the sleeve.
Another aspect of the present invention involves the sleeve being provided with a stepped portion at the middle portion of its outer periphery so that a small diameter portion is coaxially inserted into the internal bore of the cylinder cap and a large diameter portion is supported by the body and the cylinder cap by a screw connection between the body and the cylinder cap. Because the sleeve is coaxially engaged with the internal bore of the cylinder cap at the small diameter cylindrical portion, the assembling precision with respect to the guide, the cup seal, and the sleeve can be easily improved to improve the sliding performance of the first piston supported by the guide and the sleeve.
Because the large diameter cylindrical portion of the sleeve is inserted into the body and supported by the body and the cylinder cap, when the axial length of the sleeve changes due to a change in the surrounding temperature, the length change does not entirely influence the screw connected portion of the body and the cylinder cap and effectively inhibits or prevents looseness at the screw connected portion. Because the guide and the small diameter cylindrical portion are not connected, when the cylinder cap is excessively tightened, the excessive load is not added to the guide and the small diameter cylindrical portion of the sleeve (the portion with less durability of the sleeve). This makes it possible to use a reasonable material with less durability for the sleeve and the guide, which reduces the manufacturing cost.
A still further aspect of the invention involves the first communication conduit provided adjacent the rear of the cup seal and a second communication conduit provided on the cylinder cap. The second communication conduit includes an annular groove having an outer diameter larger than that of the cup seal that is formed adjacent the back face of the cup seal, opens towards the inner periphery of the cylinder cap, and is in communication with the first communication conduit and a communication bore drilled from the outer periphery of the cylinder cap to the front outer periphery portion of the annular groove, communicating with the annular groove and the reservoir connecting port, and inclined upwardly towards the reservoir connecting port. Because the first communication conduit is provided adjacent the rear of the cup seal and the second communication conduit comprises the annular groove and the communication bore, the brake fluid flows towards the first pressure chamber through the first communication conduit provided adjacent the back of the cup seal, the annular groove and the communication bore of the second communication conduit during the air relieving operation at installment of the brake master cylinder to the vehicle body.
Because the annular groove of the second conduit includes a larger outer periphery than that of the cup seal, opens to the inner periphery of the cylinder cap and communicates with the first communication conduit, and the communication bore of the second communication conduit is drilled from the outer periphery of the cylinder cap to the front outer portion of the annular groove, the brake fluid smoothly and appropriately flows through the first communication conduit and the second communication conduit during the air relieving operation. Accordingly, remaining air in the first communication conduit and the second communication conduit is appropriately relieved.
The upward inclination of the communication bore of the second communication conduit towards the annular conduit (the conduit communicating with the reservoir connecting port provided at the upper portion of the body), even when air is mixed into the brake fluid of the first communication conduit and the second communication conduit, the air reaches the annular conduit from the first communication conduit through the annular groove and the communication bore of the second communication conduit by buoyancy, is discharged to the reservoir from the annular conduit through the reservoir connecting port, and does not remain in the brake master cylinder. Accordingly, favorable performance of the brake master cylinder is maintained.
The second communication conduit includes the annular groove which is easily processed by lathe processing and the communication bore which is easily professed by drill processing formed. Because the communication bore is drilled towards the front outer periphery portion of the annular groove, processing precision in the peripheral direction is not required and this reduces the manufacturing cost.
Another aspect of the brake master cylinder of the present invention involves the first communication conduit including a communication groove provided at the front end portion of the guide slidably supporting the first piston assembled to the back portion of the cup seal in the axial direction. Because the communication groove can be formed in one unit with the guide, the guide is made of plastic material separately from the cylinder cap, which reduces the manufacturing cost.
The length of the first communication conduit, that is the length from the portion communicating with the second communication conduit of the communication groove provided at the front end of the guide to the back of the cup seal, can be shortened. Accordingly, the suction characteristic of the brake fluid to the first pressure chamber (the performance when the brake fluid is supplemented to the first pressure chamber through a lip portion of the cup seal) when the negative pressure is generated in the first pressure chamber by a sudden return of the first piston to the retracted position can be greatly improved and the performance of the brake master cylinder is accordingly improved.
In the brake master cylinder of the present invention, the first annular groove is tapered at the outer periphery gradually increasing in diameter in the forward direction. Because the first annular groove is tapered at the outer periphery in a manner gradually increasing in diameter in the forward direction, the tapered outer peripheral wall of the annular groove can properly introduce fluid therein, the flow of the brake fluid from the communication bore of the second communication conduit to the first communication conduit and the relief of air from the annular groove of the first communication conduit and the second communication conduit to the communication bore of the second communication conduit can be improved.
Another aspect of the brake master cylinder of the present invention includes an annular conduit formed between the cylinder cap and the body, positioned between the second communication conduit and the reservoir connecting port, and communicating the second communication conduit and in the reservoir connecting port. Because the brake master cylinder includes the annular conduit formed between the cylinder cap and the body, positioned between the second communication conduit and the reservoir connecting port, and communicating the second communication conduit and the reservoir connecting port, the second communication conduit provided on the cylinder cap and the reservoir connecting port provided on the body can be communicated easily and accurately by the annular conduit formed between the cylinder cap and the body.
In the present invention, the body and the cylinder cap are sealed by a first seal member assembled in a first annular groove provided on the body at the rear of the reservoir connecting port to block communication between the second communication conduit and the atmosphere. The outer diameter of the cylinder cap can thus be smaller to reduce the size and weight of the body and the brake master cylinder.
When the cylinder cap is connected to the body with screws, because the outer periphery of the first seal member assembled to the first annular groove of the body contacts the body on the fixed side, even when the first seal member receives the sliding rotation of the cylinder cap contacting the outer periphery of the cylinder cap at the inner periphery thereof, it is hard to be bent due to the stronger fixing force by the body than the rotation force of the cylinder cap, which reduces the deterioration of the sealing function. Consequently, the cross-sectional area of the seal member (effective diameter of the O-ring) can be reduced to reduce the manufacturing cost of the seal member and reduce the size of the brake master cylinder.
The body and the cylinder cap are sealed by a second seal member assembled in a second annular groove provided on the body at the front of the reservoir connecting port to block communication between the first pressure chamber and the reservoir connecting part. Thus, when the cylinder cap is connected to the body with screws, the first seal member and the second seal member are difficult to bend and the deterioration of the seal function is reduced. Accordingly, the cross-sectional area (effective diameter of the O-ring) of both seal members can be reduced to reduce the manufacturing costs of the both seal members and the size of the brake master cylinder. When assembling the cylinder cap to the body, since the both seal members provided between the cylinder cap and the body are difficult to bend against the fast rotation of the cylinder cap, it is not necessary to assemble the cylinder cap to the body by slowly rotating the cylinder cap, which shortens the assembling time of the cylinder cap to the body to improve productivity.
An annular conduit is formed between the cylinder cap and the body, and is positioned between the reservoir connecting port and the second communication conduit to communicate the second communication conduit and the reservoir connecting port. The second communication conduit provided on the cylinder cap and the reservoir connecting port provided on the body are thus easily and appropriately communicated.
The brake master cylinder also includes a flange portion restricting the retracting movement of the guide by contact with the rear end of the guide and by extending radially inwardly compared to the outer diameter of the seal member. When a first piston is pushed in the axially forward direction under the condition in which the brake master cylinder is assembled to the vehicle body and the brake fluid is filled in the cylinder housing, a piston port of the first piston passes through or is blocked by the cup seal to block communication between a first pressure chamber and a reservoir connecting port to generate pressure in the first pressure chamber. In this case, a load by the pressure of the first pressure chamber affects the guide, retraction of the guide is restricted by the flange portion of the cylinder cap, and the load affects the flange portion of the cylinder cap from the rear end of the guide to be received by the cylinder cap.
The flange portion of the cylinder cap at the rear of the guide extends radially inwardly compared to the outer diameter of the annular seal member that air-tightly and liquid-tightly seals the cylinder cap and the first piston, and is capable of ensuring sufficient contacting area with the rear end of the guide. Accordingly, excessive compression of the rear end of the guide and excessive deformation of the inner peripheral portion of the guide are prevented to ensure the integrity and intensity of the guide, to enable the use of reasonable material with less strength for the guide, and to reduce the manufacturing cost.
The brake master cylinder also includes the annular flange portion having a larger inner diameter than that of the guide. Thus, the contact between the inner periphery of the flange portion and the outer periphery of the first piston can be avoided. Accordingly, the inner periphery of the flange portion does not necessarily need to be processed (i.e., it does not require surface treatment against the abrasion caused by the sliding piston and the high precision bore processing) to reduce the manufacturing cost.
A third conduit is provided at the flange portion at the rear side thereof and is in fluid communication with a fluid chamber provided in the second cup seal, and a fourth conduit is provided in the guide member for connecting the third conduit with the first conduit. Because the third conduit is in fluid communication with a fluid chamber provided in the second cup seal and the fourth conduit is provided in the guide member for connecting the third conduit with the first conduit, air remaining in the upper portion of the fluid chamber formed with the seal member can be relieved to the first communication conduit through the third communication conduit and the fourth communication conduit.
The fourth conduit is formed by molding at the outer periphery and the rear end surface of the guide member. The fourth communication conduit can thus be easily and reasonably formed compared to machining the guide through bore processing, which reduces the manufacturing cost.
The guide used in the present invention is made of plastic material. The first communication conduit and the fourth communication conduit can thus be formed simultaneously, and by properly selecting the plastic material the surface treating against the abrasion caused by sliding piston is not necessary. This thus also reduces the manufacturing cost.